In bituminous concrete plants, various components, other than storage tanks, are present, and require heating. For example, mixing tower components, piping pumps and pugmills must be maintained at relatively high temperatures for proper operation. Furthermore, these components are liable to freeze at shut down, and have to be heated in order to be put back into operation. It has been conventional practice to utilize a circulating heat-transfer fluid, usually oil, for the purpose of heating these various plant components. The oil is commonly circulated through one or more of the storage tanks in a plant in order to take advantage of the heat provided by the storage tank heaters and stored in the asphalt contained in the tanks.
The state of the art is illustrated by the heating systems disclosed in my prior U.S. Pat. Nos. 3,622,748 and 3,681,566 and in my pending application Ser. No. 859,878.
It is a general object of the invention to provide an improved heating system of the indicated type.
Briefly stated, the asphalt heating system of the invention is comprised of a fuel fired, flue type tank heater, a heat transfer oil system for heating the oil circulated through the asphalt plant, and an electric booster heater for heating the oil and for use as a back-up for the tank heater. Control means are provided for automatically activating the electric booster heater in the event of flame failure of the tank heater.
The heating system of the invention combines the economy of fuel fired equipment with the reliability and overall efficiency that can be achieved with electric heating means. As will be described more fully hereinafter, the combination heating system of the invention including an electric booster back-up heater which is interlocked with the plant to take advantage of the lowest cost kilowatt hour charges has the following advantages:
1. It eliminates the need of overheating the asphalt in storage in order to maintain the desired temperature of the heat transfer oil.
2. It provides the ability to raise the heat transfer oil to, or above, the temperature of the asphalt in storage for heating other coiled tanks or as a back-up for heating asphalt in storage in the event of failure of the fuel fired heater.
3. It permits the heating of the heat transfer oil if there is no asphalt in the tank which allows for use of the residual in the tank in the case of an emergency.
4. It reduces the time required for heating from a cold start, thus reducing the overall consumption of energy.
5. It provides an automatic back-up of the oil heat transfer system used to heat plants in the event that the fuel fired heater fails to start.
6. It provides automatic back-up of the tank heating system to heat asphalt in storage in the event the fuel fired heater fails to start.